Targeted regulation of Rell2 by microRNA-18a is implicated in the anti-metastatic effect of polyphyllin VI in breast cancer cells.

Polyphyllin VI (PP-VI) is one of the major saponins present in Paris polyphylla Sm., a medicinal plant primarily used for cancer treatment in China and India. However, its anti-metastatic activity remains largely unknown. The current study thus investigated the anti-metastatic activity of PP-VI in mouse mammary carcinoma 4T1 and human breast cancer MDA-MB-231 cells. The anti-metastatic effect of PP-VI was investigated at a sub-cytotoxic dose in migration and invasion assays in vitro. Experimental metastasis mouse model was used to examine the anti-metastatic effect of PP-VI in vivo. Additionally, target prediction, real-time PCR, Western blotting and luciferase assay were performed to identify the target gene of a pro-metastatic microRNA, miR-18a in 4T1 cells. The effect of PP-VI on the identified target of miR-18a was further investigated. The results showed that PP-VI impaired the viability of 4T1 and MDA-MB-231 cells. Moreover, when applied at a sub-cytotoxic dose, PP-VI suppressed the metastatic potential of 4T1 and MDA-MB-231 cells. Receptor expressed in lymphoid tissue (RELT)-like 2 (Rell2) was identified as a direct target of miR-18a with anti-metastatic functions in 4T1 and MDA-MB-231 cells. PP-VI treatment resulted in increased expression of Rell2 and decreased level of miR-18a in 4T1 and MDA-MB-231 cells. PP-VI treatment also attenuated miR-18a mimic or Rell2 siRNA-augmented migration of MDA-MB-231 cells. The current work thus demonstrates for the first time that targeted regulation of Rell2 by miR-18a is in part implicated in the anti-metastatic effect of PP-VI in breast cancer cells, providing novel pharmacological insights into the anti-cancer effect of PP-VI.